Kaolin flotation process

ABSTRACT

Titanium mineral impurities are removed from Kaolin by forming an acidic dispersion of Kaolin, water and dispersing agent (acidic relative to the flotation pH), adding a collector to the dispersion, conditioning the acidic dispersion, raising the pH by the addition of reagent to the dispersion, subjecting the dispersion to a froth flotation step and recovering the Kaolin having a reduced titanium mineral impurity content.

United States Patent 1191 I Smith, III

[ KAOLIN FLOTATION PROCESS [73] Assignee: Thiele Kaolin Company,

Sandersville, Ga.

22 Filed: Nov. 2, 1970 21 Appl. No; 86,341

52 us. (:1. 209/166 [511 int. 01 ..B03d 1/02 58 Field 6: Search 209 166,1 7

[56] References Cited UNITED STATES PATENTS 2,249,570 7/1941Lane,....'......; 209/166 .1451 July 10, 1973 3/1969 Oliver 209/5 6/1969Condy 209 5 Primary Examiner-Frank W. Lutter Assistant Examiner-Robertl-lalper Attorney-Merriam, Marshall, Shapiro & Klose 57 ABSTRACTTitanium mineral impurities are removed from Kaolin by forming an acidicdispersion of Kaolin, water and dispersing agent (acidic relative to theflotation pH), adding a collector to the dispersion, conditioning theacidic dispersion, raising the pH by the addition of re agent to thedispersion, subjecting the dispersion to a froth flotation step andrecovering the Kaolin having a reduced titanium mineral impuritycontent.

15 Claims, No Drawings 1 KAOLIN FLOTATION PROCESS The present inventionrelates to a process for removing discoloring mineral components fromaluminosilicious components such as kaolin clay. More particu larly, thepresent invention relates to a process of removing titanium mineralimpurities from kaolin clay by a novel and improved method of frothflotation.

Titanium mineral impurities naturally occur in many kaolin clays, andsuch mineral impurities cause a color in the clay which detracts fromthe appearance of the clay. The prior art has proposed many systems forremoving the impurities, including froth flotation sys terns. Such priorart processes generally involve forming a suspension or slurrycontaining clay, water and dispersing agents, raising pH of the slurryof the clay to an alkaline value, such as by the addition of ammoniumhydroxide and other reagents and subjecting the slurry to a frothflotation process. In general, the froth flotation processes of theprior art comprise adding a collector such as for example oleic acid tothe alkaline slurry of the clay, conditioning the slurry by agitatingthe slurry in a tank for a time to dissipate energy in the clay, addinga frothing agent such as pine oil to the conditioned slurry, and thenpassing air through the slurry in a known manner.

The prior art froth flotation processes have had difficulty ineconomically floating clays which contain a high proportion of fineparticles. For instance, clays which contain greater than about 40percent by weight of particles finer than about 2 microns equivalentspherical diameter, or smaller, have been difficult to clean up usingprior art flotation processes. Various solutions to this problem havebeen proposed including U.S. Pat. No. 2,894,628, which describes the useof various activators, and U.S. Pat. No. 3,450,257, which describes thedissipation of large quantities of energy into the clay slurry prior tothe froth flotation step.

The present invention is directed to an improved method of frothflotation which not only removes an equal or greater amount of thetitanium mineral impurities than the prior art process, but whichresults in the recovery of a higher percentage of clay product than ispossible through the use of the prior art processes.

The present invention is accomplished by forming an acidic aqueousslurry of the clay containing the titanium mineral impurities, usingconventional dispersing agents in the conventional amounts. The pH ofthe slurry must be acidic relative to the pH at which the flotationtakes place. A conventional amount of tall oil or similar collector isthen added to the acidic slurry and the slurry is conditioned byagitation. The amount of conditioning used will vary with the exact typeof clay being processed, but for most clays it is preferred to conditionin a high intensity mixer for about l minutes, in addition to the timerequired to mix in the reagents. However, for some fractions of someclays, lesser amounts of energy input give satisfactory results. Afterthe conditioning step, the pH of the slurry is raised to an alkalinevalue, preferably between about 8 and 10, and the slurry is subjected toa conventional froth flotation step. Simply stated, the presentinvention departs from the prior art in that after the collector isadded, the conditioning step is carried out at an acidic pH, the pH isthen raised to an alkaline value whereupon the slurry is floated. Theprior art proce dure, wherein the slurry containing the collectors wastreated with alkaline material prior to the conditioning step, seemedlogical since the alkaline material would tend to saponify thecollectors which were generally tioning at the acidic pH, and theagglomeration facili tates the subsequent removal of the impuritiesduring the froth flotation step. It is postulated that the improvementresults from agglomeration to form larger particles which are easier toremove in the froth flotation step. The apparent agglomeration makes itpossible to use a somewhat lower proportion of reagents than isgenerally recommended by the prior art.

Briefly, the preferred mode of the present invention requires theproduction of a clay-water slurry at about 40 percent by weight solids.Sufficient sodium silicate is added to deflocculate the clay and thesodium silicate is mixed into the slurry. Next lead acetate, anactivator, is added to the slurry with further mixing. Tall oil, whichacts as a collector for the titanium dioxide, is then added and mixedinto the slurry. The slurry must be acidic with respect to the flotationpH at this point in the process. The slurry is subjected to high energyconditioning from about 5 to about 60 minutes. Following theconditioning, sufficient ammonium hydroxide is mixed into theconditioned slurry to raise the pH in ex cess of 9.0. The slurry isdiluted to about 20 percent solids and fed into a flotation cell whereinthe impurities are floated off and the purified clay is recovered.

Although the examples set forth below are largely directed to flotationprocesses carried out on crude clay, the present invention contemplatesthe use of the process in connection with refined clay, partiallyrefined clay, and blends of refined clay and crude clay. For instance,very dramatic results have been obtained by applying the process of thepresent invention to a coarse clay, which is the reject from'a processwhich removes coating grade clay from a crude clay. Further, a coarseclay fraction resulting from the removal of coating grade clay andfiller grade clay from a crude clay may be used. Good results have beenobtained using blends of crude clay and the coarse clays describedabove.

The present invention is particularly useful for brightening the coarserfractions of kaolin clay, although whole crude clay, prior tofractionation into various particle size fractions, can be substantiallybrightened by the use of the present invention. However, the flotationoperation of the present invention is not as effective when the clayfeed is of too fine particle size. My invention is particularly suitablefor the treatment of such coarser clay kaolin fractions as exemplifiedby those clays of commerce not containing more than about 30 percent byweight of 2 micron (equivalent spherical diameter) particles and notmore than about 15 percent by weight of --1 micron particles, and forthe treatment of crude kaolin before any fractions are removed. Further,the present invention has proved to be useful in treating whole crudeclay, which is subsequently fractionated to produce a high brightnesscoating grade clay.

It has been found that most kaolins, when made up in aqueous dispersionare acid in that they are below 7.0 pH. Most kaolin, when made into adispersion using sodium silicate will have a pH of about 6.5. Althoughsome kaolins are alkaline in the absolute sense and will yielddispersons of as high as 8.0 pH, slurries made from such kaolins areacidic with respect to the pH at which the flotation step is carriedout. As is more fully explained below, the flotation step is preferablycarried out at about 9.0 to 10.0 pH.

In carrying out the present invention, the initial dispersion must beacidic with respect to the pH at which the flotation takes place. Formost clays, using conventional dispersing agents, upon forming anaqueous dispersion, the initial pH will be below 7.0 and for most claysit is unnecessary to adjust the naturally achieved acid pH. However, thepresent invention contemplates adjusting the pH, either by adding acidicor alkaline reagents to the initial dispersion. Since the best resultshave been achieved with clay dispersions of less than 7.0 pH, it isusually not advantageous to raise the pH and little advantage has beenobserved in lowering the pH ous slurry before the flotation reagentsareadded. Generally speaking the slurry used to admix the reagents and tocondition the slurry should be about 40 percent by weight clay solids.Although higher or lower solids content slurries can be used, it isgenerally considered necessary to use a slurry containing about between30 and 70 percent by weight solids in order to get efficientconditioning after the addition of the reagents. Some of the bestresults have been achieved by conditioning at between 60 and 70 percentsolids. Slurries containing less than about 30 percent by weight ofsolids seem to require the use of more energy to give the clay particlesthe same degree of conditioning. Higher solid slurries, are moredifficult to handle and become unpumpable as solids content rise muchabove 70 percent by weight.

The kaolin clay which is purified and brightened by the presentinvention is dispersed using conventional dispersing or deflocculatingagents such as sodium hexameta-phosphate, sodium carbonate, sodiumsilicate, or combinations thereof. These reagents are used inconventional amounts and from about 0.2 to about 20 pounds per ton havebeen found satisfactory. As is described in the examples, sodiumsilicate is the preferred dispersing agent, and from about 4 to lbs. perton are generally preferred.

In carrying out my flotation treatment, any of the well-known negativeion collectors, such as a fatty acid or a fatty acid salt, may be used.I prefer to use tall oil (an oleic acid product of vegetable extraction)as the collector because of its relatively low cost. However, anyequivalent negative ion collector, such as red oil (oleic acid of animalsource) may be employed. The present invention also comtemplates the useof a number of different anionic oleophilic collector reagents includingcoconut oil fatty acids, linoleic acid, stearic acid,'lauric acid, resinacids, sulpho-oleic acid, the petroleum sulfonates such as AmericanCyanamids reagent 825, and alkali or ammonium salts of such materials.The present invention contemplates the use of only a small portion ofsuch collector reagents. It has been found that from about 0.02 to about1 percent by weight of the collector reagent, based on the weight of thedry clay, should be used. This range is equivalent The clay which is tobe treated is made up in an aquefrom about 0.4 to about 20 lbs. per ton.The preferred range for the collector is from about 1 to 6 lbs. of talloil per ton of clay, with the optimum shifting within that range,depending upon the clay feed used. Higher amounts of the collector oilmay be used and the removal of titanium mineral impurities isfacilitated thereby, but there is a tendency to leave some of the oilycollector as a residue in the clay. The presence of the oil in the clayis, of course, undesirable since it reduces the brightness. The higheramounts of collector reagent also tend to make the floated clay foamy.

In the flotation of some clays, it has been found highly desirable toadd an activator. Generally speaking, the present invention contemplatesthe use of an activator which is provided by adding to the claydispersion a small amount of a water soluble salt of a metal of Group IIor higher in the Periodic Table. Although the activator ions used by theprior art including magnesium, calcium, strontium, barium, or mixturesof these may be used, the best results have been achieved using leadion. It has been found convenient to use lead acetate as a source ofa'lead ion. A small amount of activator is adequate. For instance, fromabout 0.5 to 1.0 pound of lead acetate per ton of clay gives goodresults.

The feed kaoline slip will normally contain some of the requiredactivator ions, chiefly calcium ions, by derivation from the kaoline asmined, or the water used in processing. The deficiency in the amount ofactivator ions may be corrected by the addition of the required amountof an oxide, salt, or hydroxide of magne sium, lead, calcium, strontium,or barium. The added quantity of the compound must be sufficientlysoluble to dissolve in water present in the slurry mixture, but caremust be taken to avoid raising the pH of the slurry to an alkalinevalue. For some clays, no additional activator is required.

In practicing the present invention, it is essential to condition theaqueous dispersion after the collector and the activator have been addedto the slurry, but before the addition of major portions of the alkalinereacting reagents. It is essential that a major portion of theconditioning step, and preferably at least percent ore more of theconditioning, be carried out at an acid pH or at a relatively acid pH.It has been found that the preferred range is from about 5.5 to 7.0 pHfor carrying out the conditioning treatment. The conditioning treatmentis carried out by agitating th mixture of clay, water, collectorreagents and activator ions from about 5 to about 60 minutes, althoughbetween about 10 and 20 minutes is usually suitable. While it isessential that the major portion of the conditioning take place at anacidic pH, and it is preferred that at least 75 percent of theconditioning take place at an acidic pH, a short conditioningimmediately prior to the flotation step (as illustrated in Example I,for instance) is contemplated by the present invention. It is essentialthat at lease some portion of the conditioning take place at an acid pHafter the collector reagent has been added to the slurry, but prior tothe addition of the alkaline reagents.

In the conditioning step, any intensity of agitation that will producegood mixing will suffice, but for optimum results a high intensity mixeris preferred. Such high intensity mixing may be obtained by using highspeed Cowles mixer, a colloid mill, a Kady Mill or the like. While anlnframo mixer (a low intensity mixer) may be used for mixing thedispersing agent, the collector, and

step. The Inframo mixer has been demonstrated to be adequate forconditioning some coarse clay fractions, but high intensity conditioningis essential for all fine clays and most coarse clays too.

After the slip has been conditioned, the slurry is prepared for theflotation step. it is essential that the flotation take place at analkaline pH. Therefore, it is necessary to raise the pH from the acidicvalue at which the conditioning was conducted to an alkaline value bythe addition of an alkaline reagent. Although various alkaline reagentsmay be used, ammonium hydroxide has produced excellent results and isgenerally preferred. Preferably the flotation is carried out at a pHbetween 9 and 10, although higher or lower values can be used on someclays. Preferably the flotation process is carried out after dilutingthe slip to approximately percent by weight solids. Again, higher orlower percentages of solids can be used in the flotation step, althoughgenerally between 15 and percent by weight solids are preferred.

In carrying out the present invention it is desired that no frothingagent be employed. It'has been found that the addition of the frothingagent to the slurry following the conditioning step, such as is usuallydone in the prior art, is not necessary, and merely adds to thematerials which must be removed from the clay slurry prior to the timeit is sold. done The following examples serve to illustrate theflotation of kaolin using several specific activators and tall oils, butit is understood that these examples are set forthmerely forillustrative purposes and many other reagents are within the scope ofthe present invention.

EXAMPLE I A clay slurry was prepared from 2,000 grams of dry. clayobtained from a mine in Washington County, Ga.

The clay was dispersed in water using 8.5 pounds per ton of N-bandsodium silicate and sufficient water to produce a slurry containing 40percent by weight solids. This was mixed for 5 minutes in a CowlesDissolver, a high energy mixer, whereupon 0.5 pounds per ton of leadacetate was added. The slurry was again mixed for 5 minutes in a CowlesDissolver, whereupon 3 pounds per ton of tall oil were added. Followingthe tall oil addition, the slurry was conditioned in a Cowles Dissolverfor about 5 minutes. Following the conditioning step, 3 pounds per tonof ammonium hydroxide was added in order to give a pH of 9.4. The slurrywas conditioned 5 additional minutes with the Cowles Dissolver anddiluted to 20 percent by weight solids, transferred to a flotation celland floated for minutes.

After floating, 86 percent of the clay containing 1.14 percent by weightTiO was recovered. This product was settled to a coating grade clay,flocced with sulfuric acid, bleached with 4 pounds per ton of sodiumhydrosulfite, filtered and dried to produce a clay having a GEbrightness of 86.8.

A control sample, which was not floated, contained 1.81 percent titaniumdioxide and had a GE brightness after settling and bleaching of 86.0.

A similar experiment wherein the ammonium hydroxide was added prior tothe conditioning step produced a similar product, but only 45 percent ofthe clay containing 1.43 percent by weight TiO was recovered.

EXAMPLE "A Using the same clay described in Example 1, contain ing 1.81percent titanium dioxide, the process of the present invention wascarried out. All mixing was done in a Cowles Dissolver. A slurry wasmade up at 40 percent solids using 8.5 pounds per ton of N-brand sodiumsilicate to give a slurry having a pH of 6.0. After mixing for 5 minutes0.5 pounds per ton of lead acetate was added and mixed for 5 minutes: togive a pH of 5.9. Three pounds per ton of tall oil was-then added to theslurry to give a pH of 5.7. The slurry was subjected to a 5 minuteconditioning step as shown in Example I, using the Cowles Dissolver.Then 3 pounds per ton of ammonium hydroxide was added to give a pH of9.4. The slurry was given an additional 5 minutes conditioning and wasthen diluted. After dilution to 20 percent solids the pH was still 9.4,whereupon the slurry was fed to the flotation cell. The resultingproduct contained 1.24 percent titanium dioxide and represented arecovery of 86 percent of the clay. The clay was settled, flocced andbleached to give a GE brightness of 87.3.

EXAMPLE HE A similar test was run to that described in Example 11Aabove, but prior to the addition of the lead acetate, 0.75 pounds perton of ammonium hydroxide was added to the slurry. After the addition ofthe lead acetate and the tall oil the pH of the slurry was 6.5. Thematerial was subject to conditioning at 6.5 pH. After the conditioningstep, additional ammonium hydroxide was added to raise the pH to 9.1.The slurry'was diluted to 20 percent solids, whereupon the pH was 9.0.Flotation of the material gave a recovery of 69'percent of a productcontaining 1.20 percent titanium dioxide. The brightness wasapproximately the same as that achieved by Example 11A. f l

EXAMPLE lll Example 111 was run using a process similar to Examples Iand 11 except no lead acetate was used as an activator, and 8 pounds perton N-brand sodium silicate instead of 8.5 pounds was used. Also, asimilar but different sample of clay from the first two examples wasused. Several runs were conducted in which the condi-. tioning wascarried out at different pH levels by adding varying amounts of ammoniato the slurry prior to the addition of the tall oil.

Table 111 A B C D Control pH after Silicate Addition 5.8 5.8 5.8 5.8Pounds of Ammonia 0 0.75 1.50 2.25 pH after Ammonia 5.9 6.4 7.4- Phafter Tall Oil 5.7 6.2 6.7 pH after All Ammonia 8.2 7.9 8.0 7.9 pH afterDilution to 20% solids 8.5 8.2 8.3 8.3 TiO, in Product 0.93 1.11 0.860.91 1.55 Recovery 86 84 84 84 (LE. Brightness* 88.6 86.1 88.2 87.8 87.0

" Brightness measured on settled clay.

EXAMPLE IV The clay used for this example was a typical kaolin fromWashington County, Ga. containing 1.69 percent TiO by weight. 13,320grams crude clay (10,000 grams dry clay) were blunged to around 63percent solids using a Cowles type mixer and 4 pounds per ton N brandsodium silicate with 8 minutes blunging time. This was settled 2 minutesper inch to remove sand. 2,000 grams of this degritted crude was dilutedto 40 percent solids and 1 pound per ton N-brand silicate was added andthe slip stirred for 5 minutes with an lnframo mixer (low energy). Onepound per ton lead acetate was added and the slip was stirred anadditional 5 minutes. Three pounds per ton tall oil were added to give apH around 6.5 and the slip was conditioned 20 minutes using a highintensity Cowles type mixer. After this conditioning 4 pounds per tonaqueous ammonia were added and the slip was stirred 5 minutes using thelnframo mixer yielding a 9.8 pH. This slip was diluted to 20 percentsolids in the flotation cell giving 9.6 pH, and floated for 30 minutesremoving a discolored froth. After 30 minutes the cell was drainedgiving 87 percent recovery and 0.5 percent TiO The product was settledto approximately 80 percent 2p. particle size, flocced, bleached with 3pounds per ton sodium hydrosulfite, filtered, and dried. This settledclay had a brightness of 89.8 compared to 85.8 on the not floatedcontrol sample. 7

Example V shows another flotation test using the same crude clay feedused inExample IV. The pH was checked moreoften in Example V, and acontrol sample was run.

EXAMPLE V The sample conditioned at'acid pH with the tall oil presentwas run as follows. 2,660 grams crude clay (2,000 grams dry) wereblunged 8 minutes at approximately 60 percent solids with 5 pounds perton N-brand sodium silicate. This was settled 2 minutes per inch toremove the sand. This clay had a 6.5 pH. One pound per ton additionalsilicate was added and stirred 5 minutes with the lnframo mixer giving7.0 pH. One pound per ton lead acetate was added and water to cut thesolids to 40 percent. This was stirred 5 minutes with the lnframo giving6.8 pH. Three pounds per ton tall oil were added and the slip wasconditioned 23 minutes on a Cowles mixer at 2,100 rpm with a 4 inchCowles blade; This gave 6.8 pH. Four pounds per ton ammonia were addedand the conditioned slip was cut to 20 percent solids and floated 30minutes removing a discolored froth. The clay was drained from the cellyielding 80 percent recovery and 0.62 percent TiO This product wassettled to 81 percent -2p. particle size, flocced, filtered, reslurriedto around 20 percent solids, bleached with 3 pounds per ton sodiumhydrosulfite, filtered, and dried. This gave a brightness of 90.1.

CONTROL FOR EXAMPLE V The control sample with the ammonia added beforeconditioning was run as follows. 2,660 grams crude clay (2,000 gm dry)were glunged- 8 minutes at approximately 60 percent solids with 5 poundsper ton N-brand sodium silicate. This slip had a 6.6 pH after settling 2minutes per inch to remove sand. One and one tenth pound per tonadditional silicate was added and the slip was stirred 5 minutes withthe lnframo mixer giving 7.3

pH. One-and-one-tenth pound per ton lead acetate was added and water tocut the solids to 40 percent. This was stirred 5 minutes with thelnframo giving 6.9 pH. Four pounds per ton ammonia were added andstirred 5 minutes with the lnframo giving 9.9 pH. Three pounds per tontall oil were added and the slip was conditioned 20 minutes on a Cowlesmixer at 2,000 rpm with a 4-inch Cowles blade. This gave 9.4 pH. Theconditioned slip was cut to 20 percent solids and floated coarse clay.All of the conditioning for Examples VI through [X was done with a lowenergy inframo mixer.

EXAMPLE VI A crude kaolin from Washington County, Ga. was mined andrefined using a conventional commercial process. After removal of a No.2 coating clay, the coarse reject remaining was used for this test. Thisfeed clay contained 1.42% TiO One-half pound of calgon per ton andone-half pound soda ash per ton were added to 2,000 grams of clay andmixed for 5 minutes with an inframo mixer at 40 percent solids. Threepounds of tall oil per ton were added and the slip was conditioned for 5minutes. Three pounds of ammonia per ton were added and the slip wasmixed S'minutes with the inframo giving 9.8 pH. Five thousandmilliliters of water were added cutting the solids to 20 percent and thepH to 9.5. The conditioned clay was subjected to froth flotation for 30minutes removing a discolored froth. After floating, the clay contained0.45 percent TiO and represented a percent recovery.

EXAMPLE v11 Another sample of a coarse clay fraction remaining afterseparating a No. 2 coating clay from production was used for thisexample. The feed clay contained 1.29 percent TiO Two thousand grams ofdry clay were mixed at 40 percent solids with 4 lb./T N brand silicateand an inframo mixer. One-half pound of lead acetate per ton was added,the slip was mixed 5 minutes, and 3 pounds per ton of tall oil wereadded. After conditioning for 5 more minutes, 4 pounds per ton ofammonia were added and the sample mixed 5 additional minutes with theinframo mixer giving 10.1 pH. Five thousand milliliters of water wereadded giving 20 percent solids and 9.8 pH. The sample was floated 30minutes yielding a product with 90 percent recovery and 0.41 percent TiOEXAMPLE V111 A sample of clay from Washington County wasSeventeen-hundred-twenty grams of this coarse clay were blunged minutesat 40% solids with 0.25 pounds per ton of calgon and 0.25 pounds per tonof soda ash using an inframo mixer. Three pounds of tall oil per tonwere added and mixed with the inframo mixer for 5 minutes. Three poundsof ammonia per ton were added and mixed 5 minutes giving 9.8 pH.Forty-threehundred milliliters of water were added cutting the percentsolids to percent and the pH to 9.5. The conditioned clay was floatedfor 30 minutes removing a discolored froth, after which the cell wasdrained yielding a product with 91 percent recovery and 0.42% TiOEXAMPLE IX A sample of coarse reject remaining after a No. 2 coatinggrade clay was removed was used for this example. The feed materialcontained 1.33% TiO Two thousand grams of clay were blunged at 40percent solids and flocced to a 3.6 pH with sulfuric acid. After 8minutes mixing with the inframo mixer 3 pounds per ton of tall oil wereadded and the slip was conditioned 5 more minutes. Two pounds of N brandsilicate per ton were added giving 4.9 pH, and after conditioning 5minutes 3 pounds per ton of ammonia were added. After 5 minutes furthermixing in the inframo mixer, the pH was9.3. Five-thousand milliliters ofwater were added cutting-the solids to 20 percent and the pH to 9.0. Thesample was floated for 30 minutes removing a discolored froth. The cellwas drained yielding a product with 94 percent recovery and 0.60 percenTIC-2. i

A second test was run where the conditioning was done between 7 and 8 pHthat gave 71 percent recovcry and 0.80% TiO EXAMPLE X Another sample ofcoarse material remaining after a No. 2 coating grade clay was removedwas used for this example. Two thousand grams of clay containing 1.35%TiO were blunged to 40 percent solids with a Cowles type mixer andsulfuric acid was added to lower the pH to 3.5. This was mixed 13minutes with the Cowles type mixer and 3 pounds per ton of tall oil wereadded. This was conditioned 5 minutes and 2 pounds per ton of N brandsilicate were added increasing the pH to 4.8. After conditioning 5minutes we added 3 pounds per ton of ammonia and mixed an additional 5minutes at 8.9 'pHfFive-thousand milliliters of water were added cuttingthe solids to 20 percent and the pH to 8.8. The conditioned sample wasfloated 30 minutes removing a discolored froth. The cell was drainedyielding'93 percent recovery and 0.61% TiO The type of flotationmachinery employed in carrying out the present invention is notcritical, and many of the flotationmachines described in the prior artcan be used. In particular, the Steffensen flotation machine or theDenver-Sub A flotation machine, also known as Fahrenwald machine, may beused.

The flotation treatment of the present invention can be used in theplace of conventional bleaching steps, or can be employed in conjunctionwith one or more bleaching steps in which case a marked improvement inthe brightness of the final product results.

The forms of invention herein shown and described are to be consideredonly as illustrative. It will be apparent to those skilled in the artthat numerous modifications may be made therein without departure fromtitanium mineral impurities, said method comprising the steps:

A. Forming an acidic slurry having a pH from about 3.5 to less thanabout 7.0 by mixing clay, water and dispersing agents, said slurrycontaining at least 30 percent by weight of clay solids,

B. Adding to said slurry an anionic oleophilic collector for thetitanium mineral impurities,

C. Conditioning said acidic aqueous clay slurry with intense agitation,while maintaining an'acidic pl-I,

D. After at least a major portion of the conditioning, raising the pH ofsaid slurry to at least about 8.0 by adding an alkaline reagent, and

E. Introducing the conditioned aqueous clay slurry into a frothflotation cell, subjecting the conditioned aqueous clay slurry to afroth flotation pro- I cess, removing titanium mineral impurities withthe froth, and recovering clay having a reduced titanium mineralimpurities content. I

2. A method as described in claim 1, wherein an activator is added tothe slurry prior to the conditioning.

step.

3. A method as described in claim 2, wherein said activato'r is leadacetate.

4. A method as described in claim 3, wherein from about 0.5 to aboutlpound of lead acetate per ton of clay is used. I

5. A method as described in claim 1, wherein said conditioned clayslurry is diluted. to a solids content of from about 15 to 25 percent byweight prior to the froth flotation process. I

6. A method as described in claim 1, wherein the aqueous slurry containsat least 40 percent solids prior to the conditioning step. 7. A methodas described in claim 1, wherein from about 0.4 to 20 pounds per ton ofsaid anionic oleophilic collector is used.

8. A method as described in claim 7, wherein the collector is a fattyacid.

9. A method as described in claim 8, wherein said collector is tall.oil.

10. A method as described in claim 9, wherein from about l to 6 poundsof tall oil per ton of clay is used.

11. A method as described in claim 1, wherein the pH of the slurry israised to at least 9 prior to said flotation step.

12. A method as described in claim 11, wherein ammonium hydroxide isused to raise the pH.

13. In an improved method of flotation to remove titanium mineralimpurities from kaolin comprising mixing clay in the form of an aqueousslurry with sufficient alkali to raise the pH to at least about 8.0, adeflocculant, and a collector, conditioning the slurry by intenseagitation, introducing the conditioned slurry into a froth flotationcell, and subjecting the conditioned aqueous slurry to a froth flotationprocess, the improvement comprising performing at least a major portionof said conditioning of said slurry at a pH of from about 3.5 to lessthan about 7.0, prior to the addition of said alkali. I

14. A method as described in claim 13, wherein said conditioning stepfollows the addition of said collector, but prior to the addition ofsaid alkali.

15. A method as described in claim 13, wherein said slurry contains atleast 40 percent solids during said conditioning step.

2. A method as described in claim 1, wherein an activator is added tothe slurry prior to the conditioning step.
 3. A method as described inclaim 2, wherein said activator is lead acetate.
 4. A method asdescribed in claim 3, wherein from about 0.5 to about 1 pound of leadacetate per ton of clay is used.
 5. A method as described in claim 1,wherein said conditioned clay slurry is diluted to a solids content offrom about 15 to 25 percent by weight prior to the froth flotationprocess.
 6. A method as described in claim 1, wherein the aqueous slurrycontains at least 40 percent solids prior to the conditioning step.
 7. Amethod as described in claim 1, wherein from about 0.4 to 20 pounds perton of said anionic oleophilic collector is used.
 8. A method asdescribed in claim 7, wherein the collector is a fatty acid.
 9. A methodas described in claim 8, wherein said collector is tall oil.
 10. Amethod as described in claim 9, wherein from about 1 to 6 pounds of talloil per ton of clay is used.
 11. A method as described in claim 1,wherein the pH of the slurry is raised to at least 9 prior to saidflotation step.
 12. A method as described in claim 11, wherein ammoniumhydroxide is used to raise the pH.
 13. In an improved method offlotation to remove titanium mineral impurities from kaolin comprisingmixing clay in the form of an aqueous slurry wiTh sufficient alkali toraise the pH to at least about 8.0, a deflocculant, and a collector,conditioning the slurry by intense agitation, introducing theconditioned slurry into a froth flotation cell, and subjecting theconditioned aqueous slurry to a froth flotation process, the improvementcomprising performing at least a major portion of said conditioning ofsaid slurry at a pH of from about 3.5 to less than about 7.0, prior tothe addition of said alkali.
 14. A method as described in claim 13,wherein said conditioning step follows the addition of said collector,but prior to the addition of said alkali.
 15. A method as described inclaim 13, wherein said slurry contains at least 40 percent solids duringsaid conditioning step.